The first step in taking a photo is to point the camera in the right direction. But to know what that right direction is, you need a viewfinder. The problem with designing a viewfinder is that the lens on the camera is located in front of the image sensor, so it’s difficult to get your eye directly behind the lens.

SLRs get around this problem by using a flip-up mirror to bounce light into the optical viewfinder. Most digital cameras, though, simply use the LCD screen on the back of the camera to show the current framing. The new Sony Alpha SLT-A55 is a new interchangable lens camera that looks a lot like a traditional SLR. But, like a lot of its competitors, it lets you switch between the rear LCD screen and a small electronic viewfinder located where the viewfinder on an SLR would be.

The difference between the A55 and any camera that’s come before, is that Sony has placed a translucent mirror in front of the image sensor. It doesn’t move, like the mirror in an SLR, and because it’s mostly transparent, the bulk of the light coming through the lens passes on to the sensor. A tiny bit, though, gets bounced upward to the camera’s autofocus sensors. The practical upshot of this is that the camera can do what few SLRs can: continuously autofocus in Live View mode. When shooting video, this makes for a camera that handles like a point-and-shoot, but that offers the flexibility and superior image quality of an SLR.

Camera design

The A55 is a about the same size as competing mid-range digital SLRs. Small and lightweight, the camera is sturdily constructed, and offers a secure grip and well-designed interface. A big rear-mounted LCD screen flips out from the back of the camera. You can spin it around to fit it flush with the camera’s back, or tilt it up or down. It’s hinged at the bottom, rather than the side, but it still provides all the range of motion you need for above-the-head or waist-level shooting.

For self-portraits, the only way to face the screen forward is to tilt it so that it sticks straight down, below the camera. If you mount the camera on a tripod, you may not be able to see the screen when it’s sticking straight down. A proximity detector automatically switches from the rear LCD to the eye-level electronic viewfinder when you raise the camera to your eye, and the A55’s electronic viewfinder is very good, offering a big, bright, clear view of your scene.

Sony has added a really cool real-time level inside the viewfinder. As the camera tilts, a virtual horizon line shows you whether you’re level or not. Handy and non-obtrusive, the level doesn’t get in the way of the rest of the status information. All that said, I’m not a fan of electronic viewfinders, simply because their dynamic range is limited by the camera’s sensor. So, if you want to be able to see details in both bright highlights and deep shadows when you’re composing, you’ll be out of luck. This is an important consideration when weighing this camera against a traditional SLR.

As with other Sony cameras, the A55 includes a stabilized sensor, which means that any of Sony’s excellent lenses will deliver stabilized imagery. The A55 is compatiable with Sony's α lenses, Minolta lenses, and Konica Minolta AF lenses. There's an in-camera pop-up flash, as well as a iISO hot shoe mount if you'd like to use an external flash. As with other Sony DSLRs, the proprietary hot shoe mount works with Sony and Minolta products, but an adapter can be purchased separately if you'd like to turn it into a standard mount to use it with Nikon, Canon, Pentax, or Olympus accessories.

Special features

Because the A55 doesn't have to move a mirror around, Sony has been able to get a remarkable 10 frame-per-second burst rate out of the camera. It is continuously autofocusing in this mode, so fast moving subjects stay sharp. In addition to giving you a tremendous advantage when shooting sports, animals, and other fast-moving subjects, the A55's burst speed allows some other handy features. The camera's Sweep Panorama feature allows you to shoot stitched panoramic images by simply holding down the shutter button while panning across a scene. The camera automatically captures overlapping images and stitches them together, and the results are very good. No trip to Photoshop or other image editor is needed.

The A55 also offers a multi-frame noise reduction feature. If you're in low light, and are worried about your images being too noisy, this feature allows you to shoot a burst of images. The camera then combines them to create a low-noise result. Because of the camera's high burst rate, you can rattle off a few shots extremely quickly, giving you a better chance of shooting images in close registration.

While ten frames per second may not be that big a deal to photographers used to high-end, pro-level cameras, to get such speed at this price point is a real breakthrough for those who want speedy shooting.

Settings and controls

The A55 offers a full complement of auto and manual modes. Full auto, program, priority and manual modes are all accessible from the top-mounted mode dial, and controlling exposure parameters is easy and intuitive. The A55 does very well in low light, up to around ISO 6400. After that, things get pretty noisy, but Sony has included their unique multi-shot noise reduction feature, which shoots multiple images, and then combines them to reduce noise.

Surprisingly, the A55 lacks any type of Program Shift feature, for cycling through reciprocal exposures in Program mode. This is a great way to maintain some manual control while shooting in Program, and is sorely missed on the A55.

Video

The A55 shoots full 1080p AVCHD video, and shooting video with this camera is much easier than with any digital SLR. Because the camera can continuously autofocus while shooting video, you don’t need to worry about how you or your subject moves while rolling video. The camera’s quick autofocus mechanism will keep your scene in focus, even during difficult camera movements. Sony has wisely included an external mic jack, since handling the camera while shooting video generates lots of hand-holding noise.

Image and video tests

The A55 received impressively high ratings in our lab's subjective image and video tests. We tested it alongside the Sony A580 and Nikon D3100 DSLRs. The A55's scores were extremely close to the A580, and it did slightly better than the D3100. It received word scores of Very Good for exposure, color, and sharpness, but only a Good for distortion (the one category where the A580 did noticeably better).

The video quality on the A55 was one of the best we've seen on an interchangable lens camera in the past year, especially in bright light, earning a word score of Superior. Watch the sample clips from our subjective video tests (for both bright light and low light) below. Select 1080p in the drop-down menu in the lower-right corner of each player to see each clip at maximum resolution.

Macworld’s buying advice

The A55 holds its own against its competition thanks to its nice feature set and very good image quality. What sets it apart is its small side, ability to continuously autofocus while shooting video, and fast continuous shooting mode. If portability, video capability and burst shooting are serious concerns for you, then you’ll want to give this camera a very close look. If regular still images are your primary concern, then you’ll need to pay close attention to the electronic viewfinder, and try to determine if you are comfortable with its limitations.

[Macworld senior contributor Ben Long is the author of Complete Digital Photography, fifth edition (Charles River Media, 2009).]